CA1071080A - Apparatus and method for straightening elongated workpieces - Google Patents

Abstract

APPARATUS AND METHOD FOR
STRAIGHTENING ELONGATED WORKPIECES

Abstract Elongated workpieces are straightened by subjecting them to rotational bending during which plastic deformation of the workpiece occurs. The rotational bendings increase to a maximum bend of maximum plastic deformation at a sub-stantially greater rate than such bendings decrease from the maximum bend.

Description

1071~80 DISCLOSURE
The inventlon relates generally to an apparatus and method for straightening elongated workpieces of generally circular cross-sectional shape and, more particularly, to such an apparatus and method for straightening elongated workpleces by sub~ecting the workpieces to rotational bendings.
It is not always possible to maintain desired straight-ness tolerances when straightening elongated metal workpieces of generally circular cross-sectional configuration. This ~J is particularly so where the workpieces are of a material having a hlgh yleld polnt or a low modulus of elasticity, or both. Workpieces of a material having these properties elther cannot be straightened properly or cannot be straightened at all. It is also difficult to maintain desired straightness tolerances where very high accuracy is demanded such as in the further processing of bare steel rods by grinding subsequent to straightening.
Elongated metal workpieces of generally circular cross-sectional configuration are ccmmonly straightened by sub-~ecting such workpieces to rotational bendings. The rotational .

~0710l!3~

bendings may be imparted to the workpiece in a number of different ways, including the use of a two roll straightening apparatus having a rotating straightening cage. The two roll apparatus is most commonly used with solid rods or the like. For circular tubes, multi-roll straightening apparatus is commonly used, and particularly six or seven roll straight-ening apparatus. Known straightening machines of the oscillating-type are also used for straightening elongated workpieces of non-circular cross-sectional conflguratlon.
Considering a straightening apparatus from the view- -polnt of statics, the straightenlng rolls or dies may be consldered to form one or more lsosceles bending triangles for the workplece. Considerlng such stralghtening apparatus from the viewpolnt of dynamlcs, and for purposes of purely qualltatlve representatlon, the lsosceles bendlng trlangle may be consldered as a rotating envelope curve for the bendlngs to whlch a given cross-sectional slice of a work-piece is sub~ected as the workpiece passes axially through the envelope curve. In the case of rotational bendings, where the bending triangle rotates in relation to the work-plece, the envelope curve assumes the approximate shape of a double cone, with the equal diameter bases of the cones positioned together. That ls, the double cone has polnted opposite ends and the two cones have a common base located between the opposite pointed cone ends. In straight-ening apparatus Or this type, the two cones are of equal axlal length so that the common cone base is located cen-trally between the opposite polnted cone ends. Thls means that the workpiece ls sub~ected to bendlngs which increase to a maximum at the same rate that they decrease, and the

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~0'i~108 .
tol;al number of increasing bends is generally the same as the total number of decreasing bends. In addition, a relatively large number of purely elastic bendings often take place and such elastic bendings die away gradually without improvlng the straightness of the workpiece.
It is therefore the primary object of the present invention to provide an apparatus and method for straight-ening elongated workpieces of generally circular cross-sectional configuration by altering the conventional pattern of the rotational bendings to which the workpiece is sub~ected.
It is a further ob~ect of the invention to provide such a stralghtening apparatus and method wherein the workpiece is sub~ected to rotational bendings which increase to a maximum at a substantlally greater rate than they de-crease from the maximum.
It is an additional ob~ect of the invention to provide such an apparatus and method which can be used on elongated metal workpieces formed of materials having various properties.
It is a further ob~ect of the invention to provide a plurality of different types of apparatus for carrying out the improvements of the present invention.
- An aspect of the present invention resides in sub-~ectlng the workpiece to plastic deformation bends which decrease from a maximum plastic deformation bend at a substantially slower rate than they bulld up to that maximum.
The straightening results are improved with the altered bending pattern because a given cross-section of workpiece . i8 sub~ected to more plastic deformation and reverse bendlng ln the area where the bendings decrease from a maximum plastic deformation bend. This arrangement does not alter the total - -:' ' '. : . . ', . .. ' -:

10'71a~80 number of bends in the bending triangle because the total length Or the bending envelope curve is still the same.
However, the number of bends imparted to the workpiece up to the point of maximum plastic deformation bending is less than in previous arrangements, while the total number of plastic deformation bends subsequent to the maximum plastic deformation bend is substantially greater than in previous arrangements. The triangle or envelope curve in the area of decreasing bends has a more gradual slope than in previous arrangements so that there is a substantlal reduction in even the smallest degree Or residual bending which causes a slightly helical or corkscrew configuratlon in straightened workpieces.
With the flatter envelope curve in the bend die away area corresponding to the area of decreasing bends, the bearlng force of the workpiece at the outlet or runout end of the rolls is substantially smaller. This force has a significant effect upon the surface quality of the work-piece so it is desirable to reduce the force as much as possible. The force applied to the workpiece by a guide bar at the outlet or runout end of the apparatus is also reduced and this minimizes the formation of grooves in the workpiece as it runs out. A particular advantage of straightening in accordance with the present application is that the improved concepts may be used with all known straightening apparatus of the type which straighten elong-ated workpleces by lmpartlng rotational bends thereto.
In one arrangement, only the pla~tlc deformation bends decrease gradually, while ad~acent purely elastic bends die away abruptly. This makes it possible to extend that portion ~4~

,,,, __ , .. .,_._ . . ... .. ...... .. , _ .. . . . . . .

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1C~710l~0 o~ the bending envelope in which partly plastic deformation bending occurs. Therefore, more plastic deformation bends can take place ln a given bending area and this aids greatly in achieving the desired degree of straightness. In addition, this arrangement makes the envelope curve flatter or of a more gradual slope so that residual bends remaining in the workpiece are still further reduced. me number of purely elastic bends, which have no effect upon the straightness of the workpiece, is sharpely reduced in favor of more plastic deformation bends.
A straightening apparatus constructed in accordance with the present invention includes bending means for im-parting rotatlonal bendings to the workpiece. The ben*lng means may be considered as having inlet and outlet ends, and the maximum plastic deformation bend is located between such ends and substantially closer to the inlet end than the outlet end so that the bends increase to a maximum at a substantially greater rate than they decrease.
When the features of the present lnvention are used in a two roll straightening apparatus, the two rolls define the bending means and the opposite ends of the rolls generally correspond with the inlet and outlet ends of the bendlng means. The smallest diameter portlon of the concave stralghtening roll is located substantially closer to the lnlet end than to the outlet end. Thls makes the concave stralghtening roll asymmetrical, although the total length Or such roll ls not changed. The other roll of the two roll stralghtening apparatus is designed to produce an approximately equidistant straightening gap between the two rolls in the area of maximum plastic bending. Depending ~ _5_ 107~08,0 upon the curvature of the concave roll, the input end p,ortlon Or the other roll may have a smoothly curved convex shape which changes to a generally cyllndrical shape opp-osite the smallest diameter portion of the concave roll.
In other words, the other roll has a generally spherical input or inlet end portion which merges into a generally cylindrical portion at an intersection which is located opposite the smallest diameterportion of the concave roll.
In the two roll straightening apparatus, the asymmetrical design of the concave roll has the advantage of produclng a much sharper curvature or bending of the workpiece for a given radial and angular settlng of the stralghtenlng rolls. mis makes lt posslble to use a two roll stralghtening apparatus for a wlder varlety o~ workpleces, and makes such an apparatus particularly useful on small dlameter work-pleces of m~terials having a high yield point and a low modulus of elasticity because such workpieces require a conslderable amount of straightening.
In the two roll straightening apparatus, positioning the smallest diamster portlon Or the concave roll sub-stantially closer to the inlet end does not change the total length of the concave roll and thls means that existlng two roll straightening apparatus can be converted to use the features of the present lnvention. The more gradual slope of the runout portion of the concave roll also means that the output angle o~ the workpiece is substantially æmaller than prlor arrangements whereln the axis of the workpiece passes straight through the apparatus. m ls makes the im-proved apparatus very useful from the viewpoint of sub-

3 sequent finishing because the runout channel requlres only ~ot7~08Q

a slight slope.
In the two roll straightening apparatus having a concave roll with a smallest diameter portion located substantially closer to the inlet end than to the outlet end, it has been found advantageous to arrange the lengths on the opposite sides of the smallest diameter portion to have a ratio to one another of approximately between 1 to 1.4 and 1 to 2.5.
~In a two roll straightening apparatus, the rolls are obliquely positioned so that the roll axes cross one another.
With the rolls considered as being mounted one above the other, a plan view of the rolls shows the roll axes inter-secting one another at an intersection point located sub-stantially closer to the inlet end than to the outlet end.
The plvot axes of the two rolls pass through this intersection and this makes it possible to obtain an equidistant straight-ening gap in the smallest diameter region of the concave roll regardless of the extent to which the rolls are pivoted.
Most two roll straightening devlces are used for polishing as well as straightening, with the polishing being carried out in the section of greater curvature Or the workpiece between the straightening rolls, and this requires an approximately equidistant straightenlng gap between the rolls.
In a two roll straightening apparatus constructed in accordance with the present invention, the intersection of the centerllne of the workplece with the roll axes coincides with the ln-tersection of the roll axes with one another in plan view.
In accordance with another arrangement,- the desired ef~ect in a two roll straightening apparatus may be obtained 3 by tilting one of the rolls slightly out of the horizontal 10710~

toward the inlet end. In other words, the roll axes diverge ln a direction from the inlet end toward the outlet end. The rolls are also preferably positioned so that the roll axes appear to intersect one another at a location substantially closer to the inlet end than to the outlet end. This arrangement is very simple and lnexpensive, and produces good straightening results.
In one arrangement, the concave roll in the two roll straightenlng apparatus may have a surface which is shaped - in the form of two different hyperboloids on opposite sides of the smallest diameter portion. This means that the concave roll according to the present application may be produced at very low cost by conventional production methods using conventlonal machlne tools.
The improvements of the present application may also be used with a two roll straightening apparatus havlng a three-piece bottom roll and no straight edge to function as a gulde. In an arrangement of this type, in addition to the asymmetrlcal concave top roll as previously described, the increase in diameter of the central portion of the roll must be carried out from the inlet end to a point opposite from the smallest dlameter portion of the top roll, and must end there. The bender roll may be shaped so its opposite end portions take over the guide function Or a conventional straight edge.
The improved features of the present invention may also be used with straightening apparatus having three or more stralghtening rolls. In arrangements of this type, spaced-apart inlet and outlet rolls correspond generally wlth the 3o inlet and outlet ends of the previously defined bending means.
A bending tool is located ~etween the inlet and outlet rolls for lmparting the desired bends to the workpieces. The bending tool is located substantially closer to the inlet roll than to 1071~0 the outlet roll in order to produce the desired bending pattern.
In multi-roll straightening apparatus having three or more rolls, the rolls which apply the bending forces to the workpieces must be closer to ~he supporting rolls at the inlet end than to the supporting rolls at the outlet end.
Conventional six roll pipe straightening apparatus may be converted to the improved arrangement o~ the present app-lication by arranging for the smallest diameter locatlon of the central pair of the three roll pairs to be closer to the roll pair at the inlet side than to the outlet side roll pair. In effect, this transfers the roll configuration and arrangement concept of the two roll straightening apparatus to the six roll straightening apparatus. In a representatlve example, the rolls of the central pair have a distorted profile in which the smallest diameter portion is shifted toward the inlet end. It is possible to combine the two ch~racteristics of shifting the smallest diameter portion of a concave roll toward the inlet end and shifting a central pair of bending rolls closer to a pa~r of supporting rolls at the inlet end.
With straightening apparatus having three or more rolls, it is advantageous to arrange for longitudinal ad~ustment of the last roll or pair of rolls longitudinally in the direction f travel of the workpiece. This makes it pos ible to vary the deflection or deformation of the bent workpiece. Further-more, the bow at the stralghtening tool which is under the lowest stress Can be eaæily ad~usted. This advantageous arrangement has a substantial effect upon the amount of force exerted by the ad~usting mechanism.

10710~

The advantages of the present invention are par-ticularly appreciated as applied to rotating and oscillating straightening apparatus. In a special application of the present invention, a tool moving in a circular path for imparting desired bends to a workpiece is located toward the stationary clamping means at the inlet end. The significant advantages provided by this application of'the improved features of the present invention are best under-stood when considering the theoretical viewpoint. Considering the workpiece as being secured in spaced clamps on oppo~ite sides of the rotating straightening tool, it is easily seen that there are three areas in which plastic deformation of the workpiece ls approximately the sæme when the tool i8 located in a centered position between the clamps. By , shlfting the rotating tool closer to the inlet end, it is easily seen that the bendings at the outlet end decrease in proportional relationshlp to the bendings at the rotating bending tool and this greatly improves the straightening results. It may be particularly advantageous to shift the bending tool so far away from the center toward the inlet end that the ma~or plastic bending deformation occurs in the area of the b,ending tool, whereas the load applied at the support or clamp at the outlet end is purely elastic.
The elimination of the third area Or plastic derormation bending is particularly advantageous because the plastic derormation,occuring at that location is very rapidly re-duced in the vicinity Or the clamp at the outlet end. ~he ~-central bending area which,is associated with the bending tool moving in a circular path is designed in such a manner that the maximum bending or curvature of the workpiece is .
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10~7~08(~

shifted toward the inlet end. This means that the bending imparted to the workpiece, and particularly the plastic derormation bending, decreases or dies away more slowly than it increases.
The bender roll of a multi-roll straightening apparatus may be divided into two roll sections. One roll section on the bender roll is adJustable relative to the other roll section in a direction toward and away from the other roll or rolls of the multi-roll straightening apparatus. A double eccentric mechanism may be provided for achieving this ad-~ustment. An arrangement Or this type shifts the bends imparted to the workpiece over a large area of the bending zone into the plastic deformation range of the workpiece.
Therefore, there ls a reduction in the number of elastic bends which have no effect upon the straightening results.
In its basic non-ad~usted position, the ad~ustable roll section is in coaxial alignment with the other roll sectlon.
The ad~ustable roll section can be mounted on a neck ex-tending outwardly from the other roll section.
In one design for a two roll straightening apparatus~
one roll has a large bore in its inlet end face for receiving a ~ournal bearing about which the roll can tilt. The surface of the inlet end portion of the roll is approximately spher-ical about a sphere center coinciding with the tllt point of the ~ournal bearing. The outlet end portion Or the roll has a known ad~ustlng meahanism associated wlth it for ad-~usting the straightening gap between the roll~. The par-ticular advantage of this arrangement is that the roll gap on the outlet side may be ad~usted with a one-piece roll with-out simultaneously ad~u~ting the roll gap on the inlet side.

1~)7108 In accordance with another embodiment, the bending roll is smoothly curved outwardly and then inwardly at its inlet end portion to merge into a generally cylindrical central portion which extends over approximately one-third of the length of the roll. The generally cylindrical portion then merges into an inwardly curved outlet end portion. With an arrangement of this type, the partial plastic deformation imparted to the workpiece is extended because the plastic deformation bends decrease more slowly up to the transition into the elastic area. This improves the straightening results and reduces corkscrewing Or the workpiece.
Certain features of the present invention may also be used in a three roll straightening machine by dividing the slngle bending roll into two sections and using the prevlously described double eccentric arrangement for ad~usting one roll section relative to the other roll section.
For a better understanding of the present lnvention, together wlth other and further ob~ects thereof, reference ls had to the followlng descriptlon taken in connectlon wlth the accompanying drawings, and its scope wlll be pointed out ln the appended clalms.
In the drawlng:
2~ FIGURE 1 is a diagrammatic representation of a bendlng pattern lmparted to a glven cross-sectional slice of an elongated workpiece by using the apparatus and method of the present invention;
FIGURE 2 is an elevational vlew of rolls constructed 3 in accordance wlth the present lnvention for use in a two K-20~

roll straightening apparatus;
FIGURE 3 is a somewhat diagrammatic elevational view of a slx roll pipe straightening apparatus having the improved features Or the present invention incorporated therein;
FIGURE 4 is a diagrammatic elevational view of a seven roll stralghtening apparatus;
FIGURE 5 shows a special positioning o~ the rolls in a two roll straightening apparatus;
FIGURE 6 is a somewhat diagrammatlc elevational view Or a three roll straightening apparatus;
FIGURE 7 is a plan vlew Or a two roll arrangement generally corresponding to that of FIGURE 2;
FIGURE 8 is an elevational view Or a roll arrangement for a straightening apparatus having no guide bar;
FIGURE 9 is a diagrammatic elevational representation of a straightening apparatus having a rotating straightening tool;
FIGURE 10 is a diagrammatic elevational view of a two roll straightening arrangement having a split bottom roll;
FIGURE 1~ is an elevational view of a bottom bendlng roll for a two roll straightening apparatus;
FIGURE 12 is a diagrammatic elevatlonal view Or a two roll straightening apparatus having a special bottom bending roll configuration;
FIGURE 13 ls a somewhat diagrammatic elevational view Or a three roll straightening apparatus having a speclal designed bottom roll; and FIGURES 14-16 are dlagrammatic graphlcal representatlons Or straightening results obtained with the present invention as compared to the prior art.

~07:1080 Referring now to the drawing, and particularly FIGURE 1, there is shown a diagrammatic approximation of a bending pattern applied to a given cross section of a workpiece 2 as it passes through the bending zone of a straightening apparatus by moving in the dlrection of the arrow 1 with respect to a bendlng tool. The right hand portion of the workpiece 2 ln FIGURE 1 may be con-sidered to represent an inlet end Or a bending means 3 while the left hand end ln FIGURE 1 may be considered as an outlet end of the bendlng means. The pattern of the rotational bends in FIGURE 1 shows a very sharp increase or bulld up at the lnlet end ln zone 3 wherein the yleld polnt of the workpiece material ls exceeded so lt undergoes plastic deformation. Zone 3 i8 followed by a serles of decreasing rotational bends indicated generally by zone 4.
Thus 5 the rotatlonal bends build up to a maximum plastic deformation relatively rapidly and then decrease gradually from that maximum. The length ratio Or the zones 3 and 4 is approximately 0.4 to 0.7. This division of the bending area into the zones 3 and 4 results in a notlceable increase in the total number of die away or decreasing bends whlch have a materlal effect upon the straightening results. In addltlon, the rlatter or more gradual slope of the decreasing bend pattern in the zone 4 reduces the final deformatlon remalning in the workplece and thls reduces any corkscrewing of the workpiece.
FIGURE 2 shows a concave roll 5 constructed in accordance with the invention cooperating with a bottom bending roll 6.
The concave top roll 5 may be considered to have a shape 3~ comparable to that of an oversize pellet used ln an air gun.

~071~80 The concave roll 5 has two crowned end portions 7 and 8 of approximately the same maximum dlameter. The crown 8 on the inlet end of the roll 5 is followed in the direction of travel of the workpiece by a sharply inwardly tapering portion 9 which merges well before the longitudinal middle of the roll 5 into a smallest diameter roll portion 10 which is then followed by an outwardly expanding roll por~ion 11. Roll portions 9 and 11 are preferably in the form of two different hyperboloids. The bottom roll 6 for cooperation with the roll 5 may be considered as having the shape of a conventional bullet with a crowned portion 13 generally of spherical shape merging into a generally cylindrical portion 14 which terminates at a small radius 17 at the outlet end.
The bottom roll 6 ls designed in a manner to produce an equidistant straightening gap between it and the top concave roll 5 in the vlcinity of the smallest diameter portion 10 of the roll 5. As best shown in the plan view of FIGURE 7, the rolls 5 and 6 of FIGURE 2 are positioned obliquely relative to one another so that a plan view of the rolls arranged one above the other shows the roll axes intersecting at an intersection point closer to the inlet end than to the outlet end. Smallest diameter portion 10 of the concave roll 5 is opposite from the intersection of the crowned portion 13 with the cylindrical portion 14 on the bottom bending roll 6. The elongated metal workpiece of circular cross-sectional configuratlon passes between the rolls 5 and 6 in the direction of arrow 16.
The roll arrangement shown in FI~URE 3 is characterized by havlng a central pair of rolls shifted toward the inlet , ~071~130 end of the roll pairs. The distance between the roll pairs 18, 19 and the inlet rolls 20, 21 ls distinctly smaller than the distance to ad~acent outlet rolls 22, 23.
The distance between supporting inlet rolls 20, 21 and outlet supporting rolls 22, 23 is generally the same as in conventional straightening apparatus of this type.
However, the ratio of the distance between rolls 18, 19 and 20, 21, and the rolls 18, 19 and 22, 23, is approximately between 1 to 1.4 and 1 to 2.5.
A seven roll straightening arrangement is illustrated in FIGURE 4 and is characterized by having rolls 24, 25 and 26 at the inlet end, and rolls 27, 28 and 29 at the outlet end. These rolls are generally intended for clamping the workplece radially, wlth straightening roll 30 being responsible for bendlng deformation of the workpiece. As seen in the dlrection of travel of the workpiece in the directlon o~ arrow 31, roll 30 is arranged eccentrically relative to the inlet and outlet supporting rolls. me roll 30 is displaced out of the longltudinal middle of the inlet and outlet roll arrangements so that it is substantially closer to the lnlet supportlng and clamplng rolls 24, 25 and 26 than to the outlet supporting and clamping rol,ls 27, 28 and 29. m e ratio of the dlstances "
between the bending roll and the ad~acent supporting rolls ' may be approximately the same as prevlously described with respect to FIGURE 3.
FIGURE 5 shows a somewhat improvlsed arrangement whereby the bending pattern according to the inventlon may be approximated or achleved in a conventional two 3 roll straightenlng apparatus by rearranging the rolls.

Straightening rolls 32 and 33 are conventional designed rolls in a two roll straightening apparatus. The smallest d'Lameter portion of the roll 32 is located at its long-itudinal middle and the roll 33 is also symmetrical. In the view shown, the bottom bending roll 33 is slightly tilted in relation to the top roll 32 so it is inclined out Or the horizontal toward the incoming workpiece. In other words, the axes of the two rolls 32 and 33 diverge in a direction from the inlet end toward the outlet end not only in a plan view but in an elevational view as well. In a plan view, the roll axes also appear to intersect closer to the inlet end than to the outlet end. Tilting of the bottom roll axis in the manner described causes a sllght increase in the straightening gap between the two rolls on the outlet end. This roll arrangement also produces a shift of the bending forces toward the inlet end and this leads qualitatively to the results desired in accordance with the invention.
The workpiece travels in the direction of arrow 34 in FIGURE 5.
The features of the invention may also be applied to a three roll straightening apparatus as shown in FIGURE 6. In thls arrangement, inlet and outlet rolls 35 and 36 may be mounted upon a common shaft 38. An intermediate bending roll 37 is located between the rolls 35 and 36, and is located substantially closer to the lnlet roll 35 than to the outlet roll 36. The roll 36 may be axlally dlsplaceable along the shaft 38 by a known means lf so desired. All of the stralghtening rolls 35~37 have a convex outer surface, and roll 35 has a u ~

107~080 sharply tapering profile along its longitudinal section ad~acent the bottom bending roll 37. The straightening roll 37 has a sharply expanding section 4û associated with the sharply tapering profile Or the roll 35. The 5 roll 37 has its maximum diameter well ahead of its long-itudinal middle, after which it tapers inwardly with a slight curvature toward its outlet end. The working surface 39 of the roll 36 has the smallest curvature of all three rolls. The rolls are set obliquely relative 10 to one another, with bending roll 37 being displaced from a central position between the rolls 35 and 36 toward the inlet roll 35. The arrow 41 indicates the direction of entry of the workpiece between the rolls.
FIGURE 7 is a plan view of a pair Or straightening 15 rolls 42 and 43 positioned one above the other. These rolls have axes 44 and 45 which appear to intersect in a plan view of the rolls at an inter~ectlon generally indicated at 48. Centerline 46 of the workpiece movable between the rolls in the direction of arrow 47 also 20 passes through the intersection 48. The lntersection 48 ~s located substantlally closer to the inlet ends of the rolls than to the outlet ends thereof so that the length of' the rolls on opposite sides of the intersection 48 have a ratio to one another of approximately between 25 1 to 1.4 and 1 to 2.5. The intersectlon 48 is on a level with the smallest dlameter portion of the concave roll 42 whlch generally corresponds wlth the roll 5 of FIGURE 2. The plvot axes of the rolls 42 and 43 pass through the lntersectlon 48.
FIGURE 8 lllustrates a roll arrangement for use ln ~0~7~ 30 a straightening apparatus which operates without a straight edge. This roll arrangement includes a concave top roll 49 shaped in a manner corresponding to that of the rolls 5 and 42, and a bottom bending roll 50 divided into three portions. The top concave roll 49 and the bottom bending roll 50 are set obllquely to one another so that their axes appear to intersect in a plan view when the rolls are arranged one a~ove the other. Outer part rolls 51 and 52 on the bottom roll 50 are mounted eccentrically upon central roll portion 53 and are pivotable upon the eccentrics.
The end part rolls 51 and 52 engage with the top roll 49 in a manner generally similar to that of a second concave roll and perform the guide function of the straight edge in conventional apparatus. The workpiece passes between the straightening rolls in the direction of arrow 54. Outer part rolls 51 and 52 are ad~usted in order to produce be-tween them and the top roll 49 a gap which is narrower than the diameter Or the workpiece. The workpiece ad-vances with a helical motion between the rolls and enters the tapering gap in which it is laterally guided. Part roll 51 on the inlet side of the roll 50 is shorter in length than the part roll 52 on the outlet end. The part roll 51 has a sharply convex curvature. Like bottom roll 37, the part roll 53 has a sharply increasing pro-file at its inlet end which passes into a cylindrical sec-tion opposite from the smallest diameter portion of the top roll 49. As compared with the part roll 51, the part roll 52 has a slightly expanding shape which terminates with a radius at the outlet end thereof. The central roll part 53 has a sharply increasing profile on its inlet end which passes into a cylindrical section opposite the smallest diameter portion 56 of the top roll 49.

107~08~

As compared with the part roll 51, the part roll 52 has a slightly expanding shape terminating with a rad~us at il,s outlet end. The inlet end portion 55 of the central part roll 53 is located generally opposite the smallest diameter portion 56 of the top roll 49.
FIGURE 9 is a diagrammatic illustration of a ro-tating or oscillating straightening apparatus having pairs of clamping tools or rolls 57-60 and 61-64. These pairs of clamping rolls or tools are arranged on opposite sides of a straightening tool 65 which surrounds the workpiece and moves around in a circular path. The tool 65 may or may not rotate also about its own axis as it travels in a cir-cular path for imparting bends to a workpiece. Arrow 66 indicates the circular path in whlch the tool 65 travels to lmpart bends to a workplece. The tool 65 ls located between inlet clamplng rolls 59,60 and outlet clamping rolls 61, 62. The tool 65 1s positioned substantially closer to the inlet rolls 59,60 than to the outlet clamping rolls 61, 62.
FIGURES 14-16 are rather diagrammatic graphical representations of bending results obtained with the present invention as compared to the prior art. In each figure, a curvature envelope is shown at A, B or C. In FIGURES 14 and 15, this envelope is in the form of a triangle, while in FIGURE 16 it is in the form of a trapezoid. Rotation of each curve A, B or C about the abscissa will generate the curvature envelope described more fully at the beginning of the specification. In each figure, two supports or support forces are identified by I and III, while a bending force is identified by II. In FIGURE 16, an additional ad~u~table bending force I~ is added with the em~-odiments of FIGURES 10, ll and 13.

The number of plastlc deformations imparted to each cross-sectional area of the workpiece is important, as ls the amount of residual bend retained by the work-piece from the last plastic deformation bending c , c2 or C3.
By way of example, assume that a given cross-sectional area of a workpiece, at a distance "a" from the intersection of the bending curve A, B or C with the elastic limit, receives a plastic deformation component in the last bending action.
As a result, a buckling or distortion cl, c2 or C3 occurs in the workpiece. As graphically represented by FIGURES 14-16, it is easy to see that the distortion c2 or C3 is substantially less with the improved arrangements of the present invention as compared to the distortion cl produced by the prior art.
The arrangements of FIGURES 10-13 are capable of achiev-ing the results of FIGURE 16 where the plastic deformation bends rrom II to IV die away slowly, while the purely elastic bends from IV to III die away abruptly. In FIGURE 16, an additional bending force IV is necessary and the arrange-ments of FIGURES 10, 11 and 13 make it possible to ad~ust this force so it will coincide with the elastic limit of the workpiece. This force IV is also ad~ustable lndependently of forces I and II. As will appear when the description proceeds, this is accomplished by having the outlet end of the bender roll ad~ustable independently of the inlet end of the bender roll.
FIGURE 10 shows an arrangement lncluding rolls 67 and 68. The roll 67 has two opposite end portion crowns 69 and 70 merging with sharply inwardly tapering portions 71 and 72 which pass into a smallest diameter portion 73.
Convex bending roll 68 is associated with the concave roll 67, .

~71~80 and includes a main section 74 and another roll section 75 which is mounted upon a trunnion 76 of the main roll section 74 by means of a double eccentric arrangement 77 and 78. The double eccentric is located at the outlet end of the convex bending roll 68. Roll section 75 is ad~ustable toward and away from the concave roll 67 relative to the roll section 74 and is approximately one-fourth the length of the main roll section 74. The roll section 75 produces the fourth force IV of FIGURE 16. The working surface of the roll section 74 completes that part of the profile of the bending roll 68 which faces toward the concave roll 67.
FIGURE 11 shows an alternative to FIGURE 10 wherein a bottom bending roll 79 is ln one-piece but has a large bore 80 in its inlet end face receivlng a ~ournal bearing 81 of the roll frame which is not shown. The roll 79 is mounted on the ~ournal bearing 81 so the roll can tilt in all directions. The bearing and the contour of the roll are matched ln such a manner that tilting movement of the roll 79 at the roll neck 88 in the direction of arrow 82 produces no appreciable changes in the straightening gap at the inlet side. Suoh tilting movement can be effected by an ad~ustlng mechanism at the pin 88 which is not shown but ls conventlonal. At the inlet and outlet areas 83 and 84, the bending roll 79 has a sharply curved contour whereas area 85 therebetween is flatter. Roll area or section 84 produces the force IV of FIGURE 16. The center of curvature of the inlet portion 83 may lie on the surface of a sphere having its center corresponding with the center of rotation of the self-aligning bearing 87. As lndlcated dlagrammatically ln FIGURE 11, a concave roll 86 .

1~710l~(~

corresponding generally with concave roll 67 of FIGURE 10 is associated with the bending roll 79.
In the arrangement of FIGURE 11, the stralghtening gap at the inlet side is not changed with tilting of the roll 79 in the directlon of arrow 82 for ad~usting the rorce IV of FIGURE 16. This makes it possible to locate the force IV Or FIGURE 16 at the elastic limit so the sharp bend in the curve C occurs at the elastic limit.
Tilting of the roll 79 ~hanges only the outlet force IV
of FIGURE 16 by tilting the longitudinal axis of the roll 79 toward and away from the other roll 86. Due to the shape of the inlet side of the roll and due to the tilt polnt, there is no change ln the straightening gap at the inlet side.
The roll pair of FIGURE 12 lncludes a concave roll 89 shaped generally the same as the roll 67 of FIGURE 10. A
bottom bending roll 90 cooperates with the concave roll 89.
The two rolls are set obliquely to one another so that their axes appear to intersect in a plan view when the rolls are arranged one above the other. The roll 89 has sharply tapering crown sections 91 and 92 respectively at the inlet and outlet ends of the roll. The length ratio of the roll on opposite sides of the smallest dia-meter portion 93 is approximately between 1 to 1.4 and 1 to 2.5. In the direction of travel of the workpiece indicated by the arrow, sharply tapering sectlon 91 is followed after smallest diameter portion 93 with an outwardly expanding portion 94 which very gradually in-creases in diameter. The curvature of the roll 89 in~
creases again at portion 92 perceptably and a crowned _ ,. . . , ,. .. , , ~

10~710Ej 0 section 96 is arranged at the outlet end of the convçx bending roll 90 opposite from the sharply tapering section 92 of the concave roll 89. The section 96 produces the force IV of FIGURE 16. A crowned section 97 of the bending S roll 90 is arranged at the inlet end opposite from smallest diameter portion 93 of the concave roll 89. Between portions 96 and 97 of the bending roll 90 is an area 98 having a curvature which is smaller than the relevant bending line of the workpiece. The dimension "d" shows that crowned sect~on 97 at the inlet end of the roll is larger in diameter than the crowned section 96 at the outlet end of the roll. In other words, the bending roll 90 at its inlet end is curved outwardly and then inwardly to a generally cylindrical sec-tion 98 which merges into an opposite inwardly curved out-let end portion 96. The generally cylindrical portion 98 extends approximately one-third Or the length of the bending roll.
FIGURE 13 shows rolls 99 and lOO which generally correspond to the rolls 35 and 36 of FIGURE 6. Central bending roll 101 is divided longitudinally so that its design corresponds generally to that of the roll 68 in FIGURE 10. Part of roll lOlb at the outlet end is ad-~ustable radially relative to the workpiece and to the main roll section lOla by means of a double eccentric mechanism corresponding to that mechanism described with respect to FIGURE 10 for producing an ad~ustable force IV
of FIGURE 16. This mechanism is arranged on the neck 102 at the outlet end of part roll lOla in FIGURE 13., In the arrangements using divided,rolls, it is always the bending roll that is divided into sections. ,~hus, l07~aso by way of example, the divided roll may be 30 of FIGURE 4, 40 of FIGURE 6, 68 of FIGURE lO or lOl of FIGURE 13, While there have been described what are at present consldered to be the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is aimed, therefore, in the appended claims to cover all such changes and mod-ifications as fall within the true spirit and scope of the invention.

,

Claims (32)

The embodiments of the invention in which an exclu-sive property or privilege is claimed are defined as follows:

1. Apparatus for straightening elongated workpieces including bending means for rotationally bending a workpiece beyond its elastic limit, said bending means comprising rolls having spaced apart inlet and outlet ends between which the workpiece is bent to a maximum plastic deformation which builds up from said inlet end and then dies away toward said outlet end, the improvement comprising: said bending means being con-structed and/or positioned for locating said maximum plastic deformation substantially closer to said inlet end than to said outlet end so that the plastic deformation bends imparted to the workpiece decrease in magnitude more slowly than they in-crease the magnitude.

2. The apparatus of Claim 1 wherein said bending means includes a concave straightening roll having opposite end portions included in said inlet and outlet end, and said concave straightening roll having a smallest diameter portion located substantially closer to said inlet end than to said outlet end.

3. The apparatus of Claim 1 wherein a first distance is generally defined from said inlet end to said maximum plastic deformation and a second distance is defined from said maximum plastic deformation to said outlet end, and the ratio of said first distance to said second distance is approximately between 1 to 1.4 and 1 to 2.5.

4. The apparatus of Claim 1 wherein said bending means includes a pair of opposite cooperating rolls between which the workpiece is bent, said rolls having opposite end portions generally corresponding to said inlet and outlet ends, and one of said rolls being a concave roll having opposite convex roll ends and including a smallest diameter portion located intermediate said convex roll end and located sub-stantially closer to said inlet end than to said outlet end.

5. The apparatus of claim 4 wherein the lengths of said concave roll on opposite sides of said smallest diameter portion are related to one another in a ratio of approx-imately between 1 to 1.4 and 1 to 2.5.

6. The apparatus of claim 4 wherein said concave roll has the general shape of two different hyperboloids on opposite sides of said smallest diameter portion.

7. The apparatus of claim 4 wherein the other of said rolls has a curved end portion of increasing diameter from said inlet end toward said outlet end and merges into a generally cylindrical portion, and the intersection between said curved end portion with said generally cylindrical portion being located generally opposite said smallest diameter portion of said concave roll.

8. The apparatus of claim 4 wherein said pair of rolls have roll axes and are positioned above one another with said roll axes intersecting in plan view at an axis intersection located substantially closer to said inlet end than to said outlet end.

9. The apparatus of claim 1 wherein said bending means includes a pair of opposed cooperating rolls between which the workpieces pass and having roll axes, said rolls being obliquely positioned so that said roll axes diverge in a direction from said inlet end toward said outlet end.

10. The apparatus of claim 9 wherein when said rolls are positioned above one another a plan view shows said axes intersecting closer to said inlet end than said outlet end.

11. The apparatus of claim 1 wherein said bending means is constructed and positioned for abrupt termination of purely elastic bends in the bend die away area subsequent to the slow decrease in magnitude of the plastic deformation bends in the bend die away area.

12. The apparatus of claim 11 wherein said bending means includes a pair of obliquely positioned opposed cooperating rolls between which the workpieces pass, one of said rolls being divided into separate longitudinal sections one of which is adjustable toward and away from the other roll relative to the other of said sections.

13. The apparatus of claim 12 including a double eccentric mechanism for so adjusting said one section.

14. The apparatus of claim 13 wherein the other of said sections has a neck portion on which said double eccentric mechanism and said one section are mounted.

15. The apparatus of claim 11 wherein said bending means includes a pair of obliquely positioned opposed cooperating rolls between which the workpieces pass, one of said rolls having a generally spherical end portion generally corresponding with said inlet end and having an outlet roll end, said one roll being tiltably mounted on a tilting point generally corresponding with the center of a sphere on which said spherical end portion lies for tilting movement of said outlet roll end toward and away from the other said roll.

16. The apparatus of claim 15 wherein said one roll has an end face at said spherical end portion, a large bore in said end face receiving a journal bearing, and said one roll being so tiltably mounted on said journal bearing.

17. The apparatus of claim 11 wherein said bending means includes a pair of obliquely positioned opposed coop-erating rolls, one of said rolls having a generally cylin-drical portion located between opposite crown portions, one of said crown portions corresponding with said inlet end having a diameter greater than said cylindrical portion and the other of said crown portions corresponding with said outlet end having a diameter less than said cylindrical portion.

18. The apparatus of claim 11 wherein said bending means includes a roll having one roll end portion corres-ponding to said inlet end which is smoothly crowned out-wardly and then back inwardly to merge with a generally cylindrical portion and an opposite roll end portion corres-ponding to said outlet end which is smoothly curved inwardly from said cylindrical portion.

19. The apparatus of claim 11 wherein said bending means includes a roll which is longitudinally split into separate sections one of which is generally radially ad-justable relative to the other.

20. The apparatus of claim 1 wherein said bending means includes a roll having opposite end portions which are inclined inwardly toward a generally cylindrical central portion.

21. The apparatus of claim 20 wherein said opposite end portions generally correspond with said inlet and outlet ends to define inlet and outlet end portions, said inlet end portion having a length substantially less than said outlet end portion.

22. The apparatus of claim 21 wherein said inlet and outlet end portions are mounted eccentrically and rotatably on said cylindrical portion.

23. The apparatus of claim 1 wherein said bending means includes at least one inlet roll corresponding to said inlet end and at least one outlet roll corresponding to said outlet end, and a bending tool positioned generally intermediate said inlet and outlet rolls and located sub-stantially closer to said inlet roll than to said outlet roll.

24. The apparatus of claim 23 wherein said bending tool comprises a workpiece surrounding tool which moves in a circular path.

25. The apparatus of claim 23 wherein said inlet and outlet rolls comprise opposed pairs of rolls.

26. The apparatus of claim 23 wherein said bending tool comprises a bending roll.

27. The apparatus of claim 23 wherein said bending tool comprises a pair of opposed bending rolls.

28. The apparatus of claim 23 wherein said outlet roll is adjustable in the direction of travel of the workpieces.

29. A method for straightening elongated workpieces comprising the steps of; subjecting the workpieces to ro-tational bendings beyond the elastic limit of the workpiece material so the workpieces undergo plastic deformation, and applying said bendings to the workpieces so the bendings increase to a maximum magnitude more rapidly than they decrease therefrom.

30. The method of claim 29 wherein the bendings are applied to the workpieces so there are a substantially smaller number of bendings leading up to the bending of maximum magnitude than subsequent to the bending of maximum magnitude.

31. The method of claim 30 wherein said bendings are applied such that the ratio of the length over which increasing magnitude bendings are applied to the length over which decreasing magnitude bendings are applied is approximately between 1 to 1.4 and 1 to 2.5.

32. The method of claim 29 including the step of subjecting the workpieces to elastic bendings which are substantially fewer in number and decrease substantially more rapidly than said bendings which produce plastic deformation.